Wendy M. Troxel, an assistant professor of psychiatry and psychology at the University of Pittsburgh, believes shared sleep in healthy relationships can lower levels of the stress hormone cortisol and raise oxytocin, the hormone known to ease anxiety. Sharing a bed may also reduce cytokines, which are involved in inflammation.

“Sleep is a critically important health behavior that we know is associated with heart disease and psychiatric well-being,” she said. “The psychological benefits we get having closeness at night trump the objective costs of sleeping with a partner.”